Disk Drive Performance Becoming Insufficient

Posted on June 18, 2012 By Henry Newman

The latest crop of nearly SAS enterprise drives (aka enterprise SATA drives) gets between 108 MiB/sec and 132 MiB/sec of performance, while some of the fastest RAID controllers get around 40 GiB/sec. When you do the math on this, you see that the number of disk drives required to sustain this performance equals:

Near-Line Disk Average Performance

Enterprise 2.5-Inch Average Performance

20 GiB/sec controller

189.63

121.90

40 GiB/sec controller

379.26

243.81

If you take these numbers and multiply them by the size of the largest disk drives from those categories you get:

Amount of Storage

Amount of Storage in TB

567

109.8

1140

219.6

This is not a great deal of storage, especially if you are considering enterprise 2.5 inch SAS drives. Only 220 TB of space sustains the bandwidth of the 40 GiB/sec controllers. No, of course you are not going to achieve 100 percent of the bandwidth of the drives, and I am using average performance, not the performance of the inner cylinders. However, the picture is clear in my opinion, and controller bandwidth has not kept up with disk performance and density. The question is, what does this mean for the future design of controllers? Ten years ago we still had large SMP machines from a number of vendors.

My understanding is that the biggest cost for those machines was designing the memory interconnect. Today, most of those machines have been replaced by machines with NUMA memory. Interconnect performance is far less than a standard SMP of yesteryears. The new Quadcore SandyBridge/Romley systems have great I/O bandwidth, but I am afraid nothing more will be done for these designs, beyond Quadcore, to improve controller performance. I think we are going the way of the SMP vendors for the future, and controllers will be designed in clusters of boxes based on commodity hardware.

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